Chiral hybrid silica:: sol-gel heterogenisation of trans-(1R,2R)-diaminocyclohexane ligands for the rhodium catalysed enantioselective reduction of acetophenone

The synthesis of derivatives of trans-(1R,2R)-diaminocyclohexane with different substituents on the nitrogen atoms has been achieved. Rhodium complexes of these chiral ligands were evaluated as homogeneous catalysts for the asymmetric hydride transfer reduction (HTR) of acetophenone leading to moderate selectivities (ee = 0-57%). The silylation of a bromo-aryl derivative was successfully performed by a Heck's coupling reaction with vinyltriethoxysilane in the presence of a palladium catalyst. The immobilisation of this catalyst was then achieved by the sol-gel hydrolysis condensation. The resulting hybrid catalytic materials showed moderate selectivity, although much higher than the related homogeneous catalytic species. (C) 2003 Elsevier Ltd. All rights reserved.